Aigo is one of the exclamations Koreans use most often. Several theories explain its origin, but the most widely accepted traces it to the Sino-Korean word aego (哀苦). Ae (哀) means sorrowful and go (苦) means bitter or painful, so it began as a lament expressing deep grief and suffering. Over time, the pronunciation of aego is thought to have shifted to aigo. What is fascinating is that this word, which once expressed only sorrow and pain, gradually broadened in use until it became today's all-purpose exclamation — voicing joy, surprise, relief, irritation, and being moved, nearly every emotion there is.